1. PCB (Printed Circuit Board), known in Chinese as 印刷电路板, is an essential electronic component and a platform for electronic devices. Due to its method of production through electronic printing, it is referred to as a “printed” circuit board.

2. In the manufacturing process of electronic products, the production of printed circuit boards is an indispensable step. PCBs are utilized across all industries, serving as the medium through which electronic schematic diagrams can realize their designed functions, effectively transforming concepts into tangible products.

3. Prior to the invention of PCBs, circuits were created using point-to-point wiring. This method has very low reliability, as the aging of circuits can lead to breaks that result in open or short circuits. Winding technology represented a significant advancement in circuit design, enhancing durability and replaceability by winding small-diameter wires around connection points.

4. As the electronics industry evolved from vacuum tubes and relays to silicon semiconductors and integrated circuits, the size and cost of electronic components decreased significantly. This trend led to the increased presence of electronic products in the consumer market, compelling manufacturers to seek smaller and more economical solutions. Consequently, the PCB emerged.

5. The PCB production process can be summarized as follows: Cutting → Dry film and film application → Exposure → Development → Etching → Stripping → Drilling → Immersion copper plating → Solder mask application → Silk screen printing → Surface treatment → Shaping → Electrical measurement, among other steps.

Take the production process of double panels as an example:

1. Cutting

Cutting involves trimming the copper clad laminate to create a board suitable for the production line. Here, the laminate is not cut into small pieces; rather, multiple sections are arranged according to the PCB design and then cut. Once the PCB is finished, it is cut into smaller pieces.

2. Paste dry film and film.

A dry film is applied to the copper clad laminate. This film is cured using ultraviolet light to form a protective layer on the board, facilitating subsequent exposure and allowing unnecessary copper to be etched away. The blue area represents the film, the yellow represents copper, and the green indicates the FR4 substrate. Next, the film diagram of the PCB is applied. This diagram functions like a black-and-white negative photograph, mirroring the circuit design on the PCB. The film’s negative function is to block ultraviolet light from passing through areas where copper needs to remain. In the illustration, the white areas are opaque, while the black areas are transparent and allow light to pass.

3. Exposure

Exposure involves irradiating ultraviolet light onto the copper clad laminate that has the film and dry film attached. The light penetrates the dry film through the transparent sections, curing the exposed areas, while the unexposed sections remain uncured. As illustrated below, after ultraviolet exposure, the blue dry film hardens in the irradiated areas, with the purple regions showing the cured film.

4. Development

Development uses sodium carbonate (the developer) to dissolve and wash away the unexposed dry film. Since the exposed dry film is cured, it remains intact. The result is shown below, where the blue dry film has been removed, leaving the purple solidified film.

5. Etching

In this step, unnecessary copper is etched away. The developed board is treated with acid copper chloride. The copper shielded by the cured dry film remains, while the exposed copper is etched away, leaving behind the desired circuitry.

6. Removal of the film

The de-filming process involves washing off the cured dry film using a sodium hydroxide solution. During development, the uncured film is removed, while the cured film is washed away during this step. Different solutions are required to process these two forms of dry film. At this point, the circuit boards reflecting the electrical performance are complete.

7. Drilling

This step involves creating holes, including those for pads and through-holes. The picture below illustrates a PCB drill bit, capable of drilling holes with a minimum diameter of 0.2 mm.

8. Immersion copper, electroplating

During this step, a layer of copper is plated onto the pad holes and the walls of the vias, allowing the upper and lower layers to connect through the via holes.

9. Solder mask

The solder mask involves applying a layer of green oil to areas that will not be soldered, making them non-conductive. This is achieved through a screen printing process, followed by light exposure, development, and finally exposing the pads.

10. Silk screen

Silk-screen printing is used to apply characters for component labels, logos, and descriptive text onto the board.

Summary: The PCB production process is highly intricate. Taking a four-layer printed board as an example, the production process primarily includes PCB layout, core board production, inner PCB layout transfer, core board punching and inspection, as well as steps such as pressing, drilling, copper chemical deposition on the hole walls, transfer of the outer PCB layout, and etching of the outer PCB.